Recently, improvement of energy efficiency and CO2 emissions reduction is a target imposed on the automobile industries. In this context, automobile manufacturers are making continuous attempts to improve energy efficiency by using a lithium ion secondary battery having higher output and higher charging efficiency than a conventional lead storage battery.
However, a lithium ion secondary battery has a drawback that output characteristics drastically degrade when temperature drops down to a predetermined level, and this drawback of the lithium ion secondary battery is a problem that needs to be overcome to enhance cold startability of a vehicle.